Hexafluorophosphoric acid and organic sulfur compounds



United States Patent C HEXAFLUOROPHOSPHORIC ACID AND ORGANIC SULFUR COMPQUNDS Constantijn Leopold van Panthaleon Baron van Eck and Wilhelm Carel Brezesinska Smithuysen, Amsterdam, Netherlands, assignors to Shell Development Company, Emeryville, Califi, a corporation of Delaware No Drawing. Application September 22, 1952, Serial No. 310,935

Claims priority, application Netherlands November 5, 1951 9 Claims. (Cl. 260329.3)

This invention relates to novel adducts of organic sulfur-containing compounds and hexafiuorophosphoric acid methods of preparing them, and the removal of sulfur compounds from hydrocarbons, particularly petroleum hydrocarbons. A more specific aspect of the invention is the separation of mixtures of organic sulfur-containing compounds.

It is well known that the presence of sulfur compounds is detrimental to various hydrocarbon fractions for a number of reasons, such as their corrosive action, disagreeable odor, etc. The removal of sulfur compounds from gasoline is particularly important, not only for the above reasons, but also because of the adverse effect that the sulfur compounds have on the susceptibility of gasoline to the addition of tetraethyl lead for improving anti-knock quality of the gasoline.

Various processes are known for the removal of detrimental sulfur compounds from petroleum hydrocarbons. The most important processes heretofore known include hydrodesulfurization, caustic treatment, and treatment with a mineral acid, such as sulfuric acid, hydro fluoric acid, or fiuosulfonic acid. In the hydrodesulfurization process, a hydrocarbon fraction is contacted with hydrogen under conditions of elevated temperature and pressure in the presence of a hydrogenation catalyst. The organic sulfur compounds in the hydrocarbon fraction are hydrogenated to hydrogen sulfide which can then be removed by alkaline treatment, such a caustic treatment. However, this method of desulfurization is not only expensive but, in the case of cracked gasolines, the olefin content also becomes hydrogenated to a point where the anti-knock properties of the gasoline are seriously impaired. Caustic treatment of hydrocarbons is relatively expensive; furthermore, this treatment i suitable only for the removal of acidic sulfur compounds. It has recently been recognized that all types of sulfur compounds have deleterious effects on various product qualities. Therefore; caustic treatment is not altogether satisfactory. Treatment of hydrocarbon fractions with a mineral acid is often inadvisable since the acid will not only remove sulfur compounds, but also considerable quantities of hydrocarbons as well. Furthermore, such hydrocarbon constitutents as olefins and aromatics will react with a mineral acid. Treatment of cracked gasolines with mineral acids is particularly inadvisable because these stocks are degraded by loss of such anti-knock constituents as olefins and aromatics. It is obvious that a process for the removal of virtually all of the sulfur compounds from hydrocarbon fractions without substantial removal of hydrocarbons would be desirable.

The organic sulfur-containing compounds contained in various petroleum fractions include such compounds as mercaptans, including thiophenols and thiocresols; aliphatic, aromatic and cycloaliphatic sulfides and disulfides; cyclic sulfides such as polymethylene sulfides, thiophenes, penthiophenes, thionaphthenes, dibenzothiophenes, thianthrenes, and the like. It would be desirable not only Patented Apr. 16, 1957 ice to remove all of these sulfur compounds from petroleum fractions, but also to separate the various types of sulfur compounds from each other.

It is a principal object of this invention to provide novel adducts of organic sulfur-containing compounds and additaments therefor. A more specific object is to provide novel relatively oil-insoluble adducts of organic sulfurcontaining compounds containing only carbon, hydrogen, and sulfur and a suitable additament. Another object is to provide a method of fractionating mixtures of organic sulfur-containing compounds. Still another object to provide a method of removing organic sulfur compounds from hydrocarbons, particularly petroleum hydro carbons. Other objects and advantages will become apparent from the following detailed description.

In accordance with the present invention, it has been found that hexafiuorophosphoric acid forms adducts with organic sulfur-containing compounds, particularly organic sulfur-containing compounds containing only carbon, hydrogen and sulfur. More specifically, it has been found that hexafluorophosphoric acid forms adducts with hydrocarbyl sulfides, such a aliphatic, aromatic, cycloaliphatic, and cyclic sulfides. It has also been found that the formation of these adducts enables the separation of mixtures of organic sulfur compounds, as well as the removal of organic sulfur compounds from mixtures thereof with sulfur-free compounds particularly petroleum hydrocarbons and mixtures thereof.

The organic sulfur compounds which find most important application in the practice of the present invention are those which contain only carbon, hydrogen, and sulfur. These compounds can be represented by the structural formula: R(S)aR' where R represents a hydrocarbon radical, R' represents a hydrocarbon radical or hydrogen (R and R can be a single divalent group or radical forming a heterocyclic compound with (S)n) and n represents an integer from 1 to 6, inclusive, preferably 1 to 3, inclusive. The various types of sulfur compounds which are represented by the above structural formula and are suitable for the practice of the invention are: alkyl mercaptans, such as methyl, ethyl, propyl, isopropyl, butyl, amyl, heXyl, heptyl, octyl, nonyl, decyl, undecyl, dodecyl mercaptans; alkenyl mercaptans, such as propenyl and butenyl mercaptans, 2,3-butadiene-1 thiol, S-methyl-Z-butene-l-thiol, pentenyl mercaptans; cycloalkyl and cycloalkenyl mercaptans, such as cyclopentyl, cyclopentylmethyl, cyclohexyl, methylcyclohexyl, cyclohexylpropyl, cycloheptyl, and cyclopentenyl mercaptans, 2 decahydronaphthalenethiol; aryl mercaptans or thiophenols, such as thiophenol, m'ethylthiophenols, phenylmethyl mercaptans, ethylthiophenols, phenylpropyl mercaptans, indanthiols, naphthalenethiols, naphthylmethyl mercaptans, methylnaphthalenethiols, acenaphthenethiols, phenylcyclohexylmethyl mercaptans; alkyl sulfides (including polysulfides), such as dimethyl sulfides, methyl propyl sulfides, methyl butyl sulfides, dipropyl sulfides, dibutyl sulfides, butyl octyl sulfides, butyl propyl sulfides, dioctyl sulfides, butyl amyl sulfides, diamyl sulfides, methyl decyl sulfides; alkenyl sulfides (including polysulfides), such as methyl allyl sulfides, divinyl sulfides, ethyl vinyl sulfides, diisopropenyl sulfides, dibutenyl sulfides; cycloalkyl and cycloalkenyl sulfides (including polysulfides), such as ethyl cyclopentyl sulfides, ethyl cyclohexyl sulfides, ethyl methylcyclohexyl sulfides, dicyclopentyl methyl sulfides, dicyclopentenyl methyl sulfides, and decahydronaphthyl ethyl sulfides; aromatic sulfides (including polysulfides), such as ethyl phenyl sulfides, ethyl methylphenyl sulfides, propyl phenyl sulfides, ethyl dimethylphenyl sulfides, butyl phenyl sulfides, hexyl phenyl sulfides, phenyl decyl sulfides, ethyl phenylethyl sulfides, methyl benzyl sulfides, benzyl octyl sulfides,

benzyl ethyl sulfides, ethyl naphthyl sulfides, methyl naph thylsulfid'es, diph'eny-l sulfides, dinaphthyl sulfides, phenyl benzyl sulfides; cyclic sulfides, such as thiacyclopropane, thiacyclobutane, thiacyclopentane, thiacyclohexanes, thiacyclooctanes, thiophenes, methylthiophenes, ethenylthiophenes, dim-ethylthiophencs, propylthiophenes, phenylthiophenes, dibenzothiophenes, thionaphthenes, thiopyrans, benzothiopyrans, dibenzothiopyrans, thianthrenes, and the like. Other suitable compound containing only C, H, and 8 include the thioketones and thioaldehydes. It is preferred that the organic sulfur compound have not more than about 25 carbon atoms per molecule, and preferably not more than about 20 carbon atoms per molecule. The preferred compounds are the hydrocarbyl sulfides, including the polysulfides. V

The essentially neutral, i. e. non-basic or non-nitrogenous, organic sulfur compounds are also preferred. If, however, basic organic sulfur compounds are employed, an additional amount of hexafiuorophosphoric acid, equal to the base equivalent, shouid beused in the complex formation. 7

Although the above compounds are preferred, other 'organic sulfur compounds will also form adducts with tial absence of water or water vapor. When a relatively EXAMPLE =1 About 10 grams of dipropyl sulfide was dissolved in pentane, and the solution was-cooled with ice. While'the cooled solution was being stirred, 'a'solut-ionof arr-excess of HPFs in sulfur dioxide was introduced into it. Asolid precipitate was formed and most of the sulfur dioxide was allowed to evaporate. 'The precipitate was filtered oif and then washed with pentane. The pcntane was removed from the precipitate under vacuum withoutraising the temperature.

The above procedure was repeated with the following compounds: butyl octyl sulfide, benzyl octyl sulfide,phenyl dec'yl sulfide, benzothiophene, and 'dibenzothiophene. Where it proved difiicult to dissolve the compound in pentane, toluene was used.

HPF-s. Such compounds include the alkyl sulfites, such The resulting adducts were analyzed, and the pertinent as di-methyl, di-cthyl, di-propyl, di-butyl, and di-amyl data are given in Table'l:

Table I Sulfur Compound Adduct (1S cmp.: 2 HPFs) Percent 8 Percent -P Percent F M01. atlo, HPFe- So1ublIltyln com Name Pergent p theor. exp. theor. exp. the'or. exp. cale. from 91110.?1'10131 alcohol chloropercent 8 percent F torm Dlpropyl sulphide 28. l 7.8 7. 6 15. 1 15. 55, 6 56, 2 2.10:1 2. 00:1 1i- Butyloctyl sulphide. 16. 0 6. 5 (i. 8 12. 6 12. 2 46. 2 5 45-9 1;855-1 1.37:1 4- Benzyloctyl sulphide 13.5 6.1 '6.7 11.1 11.5 42.4 1.7411, 1.9211 3,- Pnenyldecyl sulphide 12.8 5. 9 6.3 11. 1 10.2 42.1 4O 8 1.77:1 "1. 87:1 so a. Benzothlopheneun 23.8 7.5 7.9 14.6 14.0 53.5 52.5 1.85:1 1.89:1 --I Dibe'nzo'thlopheno sulphide.. 17. 4 657 6. 3 13.0 '11. 8 47; 9 48.1 2. 22:1 2; 02:1

sulfites; the alkyl sulfates, such as di-mcthyl, di-ethyl, ethyl-isopropyl, ethyl-isobutyl, di-propyl,- and di-butyl sulfates; suifoxides; sulfones, and the like.

The adducts of the present invention are suitably for ed by dissolving the organic sulfur-containing compound in a suitable sulfur-free solvent, for example, a liquid aliphatic. napthenic or aromatic hydrocarbon, such as pentaue, cyclohexane, or toluene, cooling the solution to a suitable temperature, contacting the cooled solution with hexaiiuorophosphoric acid, and then separating the resulting'precipitate which is an adduct of the sulfur compound and the acid. The process can be effected in any suitable manner wherein satisfactory contacting of the sulfur compound with the acid is obtained, and wherein provision is made for separating and recovering the desired precipitate. corrosive in a free state and dissociates very rapidly at room temperature into PFa and HF, it is preferred to utilize a solution of the acid in a suitable solvent, such as sulfur dioxide, thionyl fluoride, thionyl chloride, sulfuryl fluoride, sulfuryl chloride, carbon dioxide, carbonyl chloride, audcarbonyl sulfide. The preparationof arr-anhydrous HPFs-containing composition is described in detail in the copcnding application of Mulder et al., Serial No. 277,086, filed March 17, 1952, now U. S. Patent 2,718,456, such as by the interaction of HF and PE in a suitable polar inorganic ionizing solvent for 'both the HF and PR5, such-as liquid S02 at .-l5 to C. In another embodiment of the present invention, the hexafluorophosphoric acid can be formed in s'itu. For example, the hydrogen fluoride and phosphorus pentafluoride can be introduced as separate streams-to the contacting zone-containing the sulfur compound. The formationof the adducts is also preferably carried out in the substan- As hexafluorophosphoric acid is highly It will be noted from the data in Table! that 'ithe adducts are composed of sulfur compound 'andhexafluorophosphoric acid in the approximate mole tratio of 1 m2, respectively.

The addncts can be decomposed to regenerateithe sulfur compound and HPFs by heating or by treatment with a strong base, for example, an aqueous causticxsolution. In cases where the heat necessary for regeneration may decompose the sulfur compound, it is advisable touse caustic treatment.

It has been ascertained that a critical temperature exists above which a given adduct will not form. Thus, .byra

judiciousselection of operating temperatures, ,a-mixture of twoor more organic sulfur-containing compounds, all of which form 'adducts'with HPFarcan be separated. For example, the mixture is contacted with HPFs, the treatment being carried out atintervalsofdecreasing'ternperaturesrthe adduct whichforms'at each temperature stage can then be removed from the remaining "sulfur compounds. If desired, the treatment may be carriedout'at a temperature sufiiciently low to precipitate-alloftlie sulfur compounds in the mixture. The temperituredf the resulting precipitate is then gradually raised so'th'at the decomposition of the adducts is efie'cted in stages, suitable separation of remaining adduct' and regenerated com ponents being effected at each desired stage. 'lhe're'gen-v erated sulfur compounds can "be separatedfrorh the ad ducts which are not decomposed, if neces'sary,-by the application of a solvent, such as pentane, benzene, toluene,v

5 with dibenzothiophene, which will not form an adduct. with HPFe at a temperature above about C.

It is also possible to separate mixtures of orgamc sulfur-containing compounds by contacting the mixture with HPFs at a temperature sufiiciently low to precipitate all of the sulfur compounds in the mixture, and then treating the resulting precipitate with a solvent which is selective for adducts of certain types of sulfur compounds. For example, as shown by illustrative data in Table I, chloroform acts as a selective solvent for the adducts of the dialkyl sulfides, but does not dissolve the adducts of the heterocyclic sulfur compounds. Thus, adducts of dipro pyl, butyl octyl, or benzyl octyl sulfides can be separated from adducts of benzothiophene or of dibenzothiophene, by solution of the former in chloroform.

In accordance with a'preferred embodiment of the present invention, the formation of adducts of organic sulfurcontaining compounds and HPFs is utilized in the desul furization of hydrocarbons, particularly petroleum hydrocarbons. This embodiment of the invention is applicable to the treatment of normally gaseous hydrocarbons, such as ethane, propane, butane and/ or the corresponding gaseous olefins, containing sulfur compounds, and is particularly applicable to the desulfurization of normally liquid hydrocarbon fractions, such as gasoline, kerosene, diesel oil, gas oil, fuel oil, etc.

Desulfurization of sulfur-containing hydrocarbon fractions can be effected by contacting the hydrocarbon charging stock in any suitable manner with I-IPFe, or with reagents (PF and HF) which will form HPFc in situ. The resulting adducts of the sulfur compounds and HPFs are then separated from the treated hydrocarbons. The I-IPFa is preferably applied in solution in a suitable solvent as described above. The hydrocarbon charging stock is preferably diluted with a light hydrocarbon, such as pentane, in order to facilitate separation of the resulting adducts from the hydrocarbon and to prevent contamination of the adducts with the hydrocarbon. The desulfurization may be either a batch or continuous type of operation.

Generally, the amount of HPFs applied will correspond to the composition of the adducts which are to be formed. Solid adducts are thereby formed. The solid adducts can be easily separated from the hydrocarbon in any suitable manner, for example, by filtration. If an excess amount of HPFs is employed, the resulting adducts will dissolve in the excess acid. Depending on the amount of acid employed, the resulting adducts will be partially or Wholly dissolved in HPFs. Thus, depending on the amount of acid employed, a liquid phase and a solid phase, two liquid phases, or two liquid phases and one solid phase are obtained. It is preferred to employ an amount of HPFe which will result in the formation of either one liquid phase and one solid phase, or of two liquid phases.

After separation of the treated hydrocarbon phase, from the phase containing the adducts of HPFs and the sulfur compounds, the adducts can be decomposed, as by heating, to regenerate HPFs which is then recycled to the contacting step.

Fractionation of the sulfur compounds contained in the petroleum hydrocarbon feed can be effected, as well as desulfurization of the feed, by a judicious selection of operating temperatures in the same manner as described above. For example, the desulfurization treatment can be carried out in stages at gradually decreasing temperatures; the adducts formed at each temperature stage are then removed from the mixture. According to another method, described above, the desulfurization can be effected at a temperature sufiiciently low to form adducts of substantially all of the sulfur compounds in the mixture. The resulting precipitate, after separation from the desulfurized hydrocarbons, is then gradually heated to decompose the adducts in stages, and the sulfur compound regenerated at each temperature stage is then removed from the adducts which are not decomposed, if necessary,

in the presence of a solvent which is selective for the re EXAMPLE n One hundred parts by weight of a Mexican'gas oil having a boiling range of from about 255 to about 355 C., and having a sulfur content of about 2.21% by weight in the form of organic sulfur compounds, was diluted with about 300 parts by weight of pentane. The mixture was continuously maintained at a temperature of about 0 C. During a period of about 10 minutes, a solution of about 25 parts by weight of HPFs in liquid $02 was added to the mixture with vigorous agitation. The S02 evaporated 01f almost immediately. A solid adduct of the organic sulfur compounds present in the oil was formed. In the complete absence of moisture from the air the solid adduct was filtered off through a filter of rust-proof steel. About 29.5 parts by weight of adduct wereobtaine d. M

The adduct was then decomposed by the addition of an excess quantity of aqueous caustic soda. Two layers were formed; the top layer consisted of about 12.7 parts by weight of sulfur compounds with a sulfur content of about 14.9% by weight.

The filtrate separated from the solid adduct, comprising desulfurized hydrocarbons, was washed with aqueous caustic solution. Any caustic remaining in the filtrate was removed therefrom by water-washing. The filtrate was dried and the pentane was distilled off; 84.1 parts by weight of a rafiinate, having a sulfur content of about 0.23% by weight, was obtained.

EXAMPLE 1H One hundred parts by weight of a West Texas gas oil having a boiling range of from about 280 to about 380 C., and having a sulfur content of about 1.39% by weight, was diluted with about 300 parts by weight of pentane. The mixture was contacted with a solution of about 20 parts by weight of HPFs in liquid S02 in the same manner as described in Example II. The resulting adduct was removed by filtration.

The adduct was then decomposed by the addition of an excess quantity of aqueous caustic soda. The top layer obtained consisted of about 9.0 parts by weight of sulfur compounds with a sulfur content of about 12.2% by weight.

The filtrate was washed with aqueous caustic and then water-washed. The washed filtrate was dried and the pentane was distilled off. About 88.4 parts by weight of a rafiina'te, having a sulfur content of about 0.28% by weight, was obtained.

By utilizing hex-afiuorophosphoric acid as the desulfurizing agent, loss of hydrocarbon material by reaction with or by extraction by the desulfurizing agent is substantially completely avoided.

We claim as our invention:

1. A process for desulfurizing a hydrocarbon material containing sulfur compounds which comprises contacting said hydrocarbon material in liquid phase, in the substantial absence of water and at a temperature no higher than ambient room temperature, with a solution of periluorophosphoric acid (HPFs) in liquid sulfur dioxide in proportions to form solid adduct of at least a portion of the sulfur compounds and perfluorophosphoric acid, whereby such a solid adduct is formed, separating the solid adduct of sulfur compound and perfiuorophosphoric acid from the hydrocarbon material, and decomposing the adduct to separate the components thereof.

2. The process, according to claim 1, wherein the con- 7 tactingistep is carried out atv a temperature of not more than about 0 'C." l

v 3. The process, according to claim 1, wherein the hydrocarbon material is a normally liquid hydrocarbon fraction.

4. The process, according to claim 1, wherein the hydrocarbon material is a. gas oil fraction.

5. A process according to claim 1, wherein the hydrocarbon material is a liquid petroleum hydrocarbon fraction.

6. A process in accordance with claim 4, wherein the gas oil is diluted with a light hydrocarbon.

7. A' process for the separation of a mixture of at least two organic sulfur-containing compounds A and B, which'comprises contacting the mixture in liquid phase, in the substantial absence of water, with a solution of hexafluorophosphoric acid (HPFG) in liquid "sulfur dioxide under condition of temperature, no higher than ambient room temperature, and proportions of perfluorophosphoric acid and sulfur compound to form solid adduct of perfiuorophosphoric acid with essentially only sulfur compound A to the exclusion of sulfur compound B' whereby such solid adduct is formed, and separating said solid adduct from the remainder of the mixture which is enriched in sulfur compound B.

8, A process according to-claim 7, wherein the ture is one of at least two hydrocarbyl ,sulfides.

, 9. A process for the separation of a mixture of a dialkyl sulfide and a heterocyclicsul-fur compound which comprises contacting said mixture in liquid phase dis-' solved in a liquid. hydrocarbon, in the substantial ab- References Cited in the file of this patent UNITED STATES PATENTS 2,375,675 Matus'zak May s, 1945 2,488,299 Lange -a July 17, 1947 2,718,456 Mulder et al. Sept. 20, 1955 

1. A PROCESS FOR DESULFURIZING A HYDROCARBON MATERIAL CONTAINING SULFUR COMPOUNDS WHICH COMPRISES CONTACTING SAID HYDROCARBON MATERIAL IN LIQUID PHASE, IN THE SUBSTANTIAL ABSENCE OF WATER AND AT A TEMPERATURE NO HIGHER THAN AMBIENT ROOM TEMPERATURE, WITH A SOLUTION OF PERFLUOROPHOSPHORIC ACID (HPF5) IN LIQUID SULFUR DIOXIDE IN PROPORTIONS TO FORM SOLID ADDUCT OF AT LEAST A PORTION OF THE SULFUR COMPOUNDS AND PERFLUOROPHOSPHERIC ACID, WHEREBY SUCH A SOLID ADDUCT IS FORMED, SEPARATING THE SOLID ADDUCT OF SULFUR COMPOUND AND PERFLUOROPHOSPHORIC ACID FROM THE HYDROCARBON MATERIAL, AND DECOMPOSING THE ADDUCT TO SEPARATE THE COMPONENTS THEREOF. 